Broad-spectrum resistance to Bacillus thuringiensis toxins by western corn rootworm (Diabrotica virgifera virgifera).

Siva R K Jakka,Aaron J Gassmann,Ram B Shrestha

doi:10.1038/srep27860

Abstract

The evolution of resistance and cross-resistance threaten the sustainability of genetically engineered crops that produce insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt). Western corn rootworm, Diabrotica virgifera virgifera LeConte, is a serious pest of maize and has been managed with Bt maize since 2003. We conducted laboratory bioassays with maize hybrids producing Bt toxins Cry3Bb1, mCry3A, eCry3.1Ab, and Cry34/35Ab1, which represent all commercialized Bt toxins for management of western corn rootworm. We tested populations from fields where severe injury to Cry3Bb1 maize was observed, and populations that had never been exposed to Bt maize. Consistent with past studies, bioassays indicated that field populations were resistant to Cry3Bb1 maize and mCry3A maize, and that cross-resistance was present between these two types of Bt maize. Additionally, bioassays revealed resistance to eCry3.1Ab maize and cross-resistance among Cry3Bb1, mCry3A and eCry3.1Ab. However, no resistance or cross-resistance was detected for Cry34/35Ab1 maize. This broad-spectrum resistance illustrates the potential for insect pests to develop resistance rapidly to multiple Bt toxins when structural similarities are present among toxins, and raises concerns about the long-term durability of Bt crops for management of some insect pests.

Highlights

Western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is one of the most economically important insect pests of maize in the United States[1]
For all three non-Bacillus thuringiensis (Bt) maize hybrids, larval survival did not differ between field populations and control populations, whereas significantly greater larval survival was observed for field populations, relative to control populations, on Cry3Bb1 maize, mCry3A maize, eCry3.1Ab maize, and maize pyramided with mCry3A and eCry3.1Ab hybrids, indicating resistance to these Bt hybrids (Fig. 2)
Survival of western corn rootworm larvae from field populations and control populations on (a) Cry3Bb1 maize and its non-Bt near isoline, (b) Cry34/35Ab1 maize and its non-Bt near isoline, and (c) mCry3A maize, eCry3.1Ab maize, maize pyramided with mCry3A +eCry3.1Ab, and the non-Bt near isoline to these Bt maize hybrids

Summary

Introduction

Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is one of the most economically important insect pests of maize in the United States[1]. Crop losses from this pest are primarily attributed to the larval feeding on roots, which reduces yield and can complicate harvest if maize plants lodge (i.e., fall over)[2,3,4]. There are four Bt toxins that are used to manage western corn rootworm: Cry3Bb1, Cry34/35Ab1, mCry3A, and eCry3.1Ab, and these were registered by the US EPA in 2003, 2005, 2006 and 2012, respectively[8]. Cross-resistance among Bt toxins can be due to similarities in the mode of action and several studies have found cross-resistance between Bt toxins[19,20,21,22,23]

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Conclusion